Work will be concentrated primarily in the following areas: 1. Pathogenesis of immune purpura; characterization of platelet auto- and iso-antigens. Methods of detecting iso-, auto- and drug-dependent antibodies reactive with human platelets will be refined. Particular attention will be given to techniques involving Cr51 release and inhibition of platelet migration. The expression of HLA antigens on platelets and the genetic basis for its variability will be characterized. Findings will be applied to study of the pathogenesis of immune thrombocytopenic disorders, to characterization of platelet iso- and auto-antigens, and to development of improved methods of platelet transfusion therapy. 2. Molecular basis of the platelet "storage lesion". Biochemical changes occurring in platelets upon being concentrated and stored under blood banking conditions will be further characterized. Priority will be given to cyclic nucleotides and their synthetic systems and to redistribution of fatty acids among phospholipids and neutral lipids. Findings will be applied to the development of improved methods of short-term platelet preservation. 3. Molecular and functional abnormalities of "quanlitative" platelet disorders. Methodologic capabilities developed to study biochemical changes in stored platelets will be applied to platelets of patients with "qualitative" platelet disorders to determine their molecular bases. Emphasis will be placed on disorders in which platelets are "hyperfunctional" such as diabetes mellitus and type II hyperlipidemia. Findings will be utilized to increase the understanding of the role of platelets in thrombosis and vascular disease associated with these diseases. Bibliographic references: Duquesnoy, R.J., Lorentzen, D.F., and Aster, R.H.: A new method for detection of platelet antibodies: Platelet migration inhibition. Blood 45:741, 1975. Aster, R.H.: Clinical use of platelet concentrates. In Transfusion and Immunology, 1975, E. Ikkala and A. Nykanen, Eds., Vammala, 1975, p. 223.